1. Technical Field
The present disclosure relates to a smart key system.
2. Description of Related Art
In the related art, smart key systems that transmit a polling signal from a vehicle (vehicle-mounted device) to a predetermined area (for example, the vicinity of a door) outside a vehicle compartment in a fixed transmission cycle are known. In such smart key systems, if a user who possesses a portable device enters the predetermined area outside the vehicle compartment, the portable device receives the polling signal and transmits a reply signal to the vehicle. Since the vehicle-mounted device can determine that the portable device is in the predetermined area outside the vehicle compartment if the reply signal is received, certification processing of the portable device is performed. Then, when the user performs a predetermined manipulation on the vehicle after the certification of the portable device is completed (has succeeded), vehicle-mounted equipment can be made to perform a predetermined operation (for example, a locking/unlocking device of the door of the vehicle is made to perform an unlocking operation, that is, unlock the door).
In such smart key systems, a technique of offsetting the transmission timing of the polling signal by a period shorter than the transmission cycle is suggested (for example, refer to Japanese Patent Application Publication No. 2014-34768 (JP 2014-34768 A).
According to the technique disclosed in JP 2014-34768 A, in a case where noise in the same frequency band as the polling signal is output in the same transmission cycle as the polling signal from a noise source near the vehicle, the portable device can suppress a situation where the polling signal cannot be received well due to noise overlap or the like.
For example, in a case where another vehicle that transmits the same polling signal is parked adjacent to a user's own vehicle, if the transmission cycles of the polling signals of the user's own vehicle and the other vehicle are the same and the transmission timings of the polling signals also overlap each other, the portable device may be unable to receive the polling signal of the user's own vehicle. In contrast, by shifting the transmission timing of the polling signal as in JP 2014-34768 A, it is possible to avoid overlap between the polling signal of the other vehicle and the polling signal of the user's own vehicle, and the portable device can receive the polling signal.